1. Field of the Invention
The present invention relates to a zoom lens system, and more particularly to a zoom lens system having a negative front lens group, which is applicable to a wide angle zoom lens system or to a zoom lens system including in its variable field angle range the standard field angle.
2. Description of the Prior Art
In this field of art, a two-group type wide angle zoom lens system having a negative front lens group and a positive rear lens group has been known to be suitable for a zooming made of operation zoom ratio of about 2 ranging from a standard to wide field angle.
However, the lens speed of such a lens system has to be lowered to insure adequate aberration correction while the size of the lens system must be increased if the maximum field angle in the zoom range is also desired to be increased.
Further, the tolerance to any manufacturing error becomes more strict with respect to the rear lens group because of the increased aperture ratio thereof if the refractive powers of the front and rear lens groups are increased in accordance with the demand of compact size and light weight so that the rear lens group must be designed to receive a widely divergent light pencil transmitted from the front lens group of the increased refractive power.
Japanese Patent Application Laid Open No. 55-35323 also discloses a three-group wide angle zoom lens system having a negative first lens group, a positive second lens group, and a positive third lens group. However, this design approach uses only positive lens element in the first lens group and does not employ a triplet type of lens group in the second lens group. This design approach emphasizes a strong refractive power in the first lens group, a weak refractive power in the second lens group and a strong refractive power in the third lens group.
The prior art is still seeking an optimum zoom lens system that further provides a macro-focusing capability.